A great many different operating strategies and component designs are known in the field of internal combustion engines. Research and development has progressed for decades in relation to the manner in which factors such as fueling, exhaust gas recirculation, turbocharging, and variable valve actuation can be varied to produce different results. In addition to variation in these and other operating parameters, a great deal of research and testing effort has gone into the different ways that engine components, such as pistons, can be shaped and proportioned, and formed from various materials. One motivation driving advancements in combustion science and related research has been the desire to reduce relative amounts of certain emissions in engine exhaust, such as particulate matter and oxides of nitrogen or NOx. Other motivations relate to improving or optimizing engine performance, reducing fuel consumption, limiting component wear and/or fatigue and still others.
Efforts to accommodate the various different patterns of engine operation and duty cycle have resulted in the great many engine operating strategies and component designs that can be seen in the art. For certain engines that are subjected to relatively harsh operating conditions, such as high temperatures and frequent temperature swings, one area of particular research and development interest has included piston geometry and materials. Other research efforts have been directed to preparing pistons that are well-suited to conditions of relatively extreme mechanical duress. Decades of combustion science, materials, and mechanical engineering research have generally revealed that factors such as emissions and efficiency can be affected significantly and often unpredictably by seemingly minor changes in piston shape and features. Commonly owned U.S. Pat. No. 8,978,621 to Easley et al. (“Easley”) is directed to a piston having a combustion bowl shaped to balance combustion efficiency and emissions properties. The Easley disclosure proposes a piston having a compound combustion bowl and a compound rim, with an abrupt transition between the compound combustion bowl and the compound rim, with the features together desirably affecting emissions such as particulate matter and NOx, without unduly sacrificing fuel efficiency.